An electrochemical cell typically includes a cathode and an anode which participate in an electrochemical reaction to produce current. Generally, electrochemical reactions are facilitated by an electrolyte, which can contain free ions and can behave as an ionically conductive (and electronically insulating) medium.
In many electrochemical cell systems, electrode active material can precipitate in the cathode during the course of discharge or charge process. For example, in lithium-sulfur electrochemical cells, polysulfides such as S2− ions formed during the electrochemical reaction can react with Li+ ions to precipitate as solid Li2S. The slate precipitate can deposit within the pores of the cathode, which can block electrolyte from reaching electrode active material located within the pores of the cathode and reduce system performance. If large amount of Li2S precipitates on a surface of the cathode (for example, at the interface between the cathode and the separator), then a thick sheet of solid (commonly called slate) can result. This slate can plug the pores in the cathode and prevent the Li+ ions from reaching the interior of the cathode to react further. This, in turn, will cause the cell voltage to reach the end-of-discharge cut-off voltage prematurely, even though some amount of unreacted active materials are still available in the interior of the cell, which results in the reduction in the specific energy of the cathode.
The problem of excessive solid formation at unwanted locations (and the resulting pore-blocked) is not limited to lithium-sulfur electrochemical cells. For example, such solids formation can lead to problems in zinc/air, aluminum/air, lithium/air, lithium/SO2, lithium/SOCl2, and lithium/SO2Cl2, systems.
Electrodes and electrochemical cells configured to inhibit pore-blocking due to formation of solid precipitates would be desirable.